The invention relates to a method for heating the cab of a motor vehicle with a diesel engine, the cab being supplied with waste heat occurring in the diesel engine. The invention relates, furthermore, to a regulating arrangement for the cab heating and for the diesel engine of a motor vehicle, containing
a temperature sensor for the temperature of the diesel engine;
a pressure sensor for the intake pressure of the diesel engine; and
a controllable throttle valve for the supply of air to the diesel engine.
Heating systems for the cab of a motor vehicle usually obtain their heat energy from the waste heat generated in the internal combustion engine. During the starting of a motor vehicle cooled to a low ambient temperature, the problem arises that heating energy for the cab is available only when the engine has been warmed up. For this reason, additional heating systems are often provided for the cab space and can provide the necessary heat energy in the starting phase of the motor vehicle. One disadvantage of this, however, is the outlay required for the installation and operation of such an additional assembly which, as a rule, is required only for short transitional phases when the vehicle is in operation.
To speed up the warming-up of a diesel engine, it is known from JP 11324819 and JP 11-148375 to throttle or completely close the supply of air to the engine and at the same time allow intensified exhaust-gas recirculation. Intensified recirculation of exhaust gases into the inlet of the diesel engine is in this case to bring about a more rapid rise in the temperature of the engine. The measures mentioned are cut off again after a short time when a predetermined engine rotational speed is reached.
The object of the present invention was, by contrast, to provide a method and a regulating arrangement for a motor vehicle with a diesel engine, which allow the cab of the motor vehicle to be heated more rapidly from the cooled state.
In the method for heating the cab of a motor vehicle with a diesel engine, the cab is supplied with waste heat produced in the diesel engine and the temperature of the diesel engine is measured directly or indirectly. If this measured temperature is below a predetermined first limit value T1, the supply of air to the diesel engine is throttled as a result of a stipulation of a reduced intake pressure MAP_ref, until the directly or indirectly measured temperature of the diesel engine exceeds a predetermined second limit value T2.
The method is thus based, in the first place, on the fact that the temperature of the diesel engine is monitored. If this temperature is below the first limit value T1, the implementation of a special heating program is initiated. In this heating program, a reduced intake pressure MAP_ref is determined and is subsequently set by the throttling of the air supply. As a result of the stipulation of typically greatly reduced intake pressures and a correspondingly high throttling of the air supply, the pumping losses of the engine increase and the total flow rate through the engine is reduced. The two effects contribute considerably to a more rapid warming of the engine, which, in turn, is conducive to the heating of the cab. The vehicle can therefore be heated up more rapidly to temperatures which are pleasant for the occupants. It is thereby possible, under certain circumstances, to dispense with additional heating devices in vehicles which are used in regions of cold climates (for example, Scandinavia, northern USA or Canada).
Various procedures may be envisaged for determining the temperature of the diesel engine. This temperature may be determined, for example, directly via the cylinder-head temperature or else indirectly via the temperature of the coolant which is conducted through the diesel engine.
The value MAP_ref of the reduced intake pressure, which is to be set by the throttling of the air supply, is advantageously fixed by means of a predetermined table store as a function of the temperature of the diesel engine, of the engine rotational speed and/or of the engine load. The intake pressure to be set is therefore not a constant quantity, but is adapted optimally to the operating parameters of the motor vehicle.
According to a development of the method, the predetermined reduced intake pressure MAP_ref is modified as a function of the accelerator pedal position and/or of the rate of change of the accelerator pedal position in relation to MAP_ref_mod, in order to ensure that the motor vehicle has good driving properties. This ensures that the motor vehicle still reacts sufficiently to an actuation of the accelerator pedal by the driver and consequently obeys his wishes as regards driving behavior. The functions referred to may be designed, in particular, in such a way that, when a predetermined threshold value for the accelerator pedal position and/or its rate of change is exceeded, the throttling of the air supply is canceled or reduced, in order to provide the full engine power for the drive.
Furthermore, the predetermined reduced intake pressure MAP_ref is increased preferably when the air/fuel ratio falls below a predetermined minimum. This avoids the situation where the engine changes to an unstable operating state with insufficient control possibilities.
As can be gathered from the statements made above, changes to the predetermined intake pressure are necessary at the beginning and end of the heating program and, in the case of special conditions, also during the implementation of the heating program. These changes are preferably carried out in ramp form. That is to say, the respective old and new values of the intake pressure merge continuously into one another by means of a linear relation. This prevents undesirable abrupt changes in the behavior of the motor vehicle from occurring.
According to another development of the method, the exhaust-gas recirculation (EGR) of the diesel engine is closed if the temperature of the diesel engine is below the first limit value T1. This measure leads to an increased fuel consumption of the diesel engine and consequently to a more rapid rise in its temperature.
As a further conducive measure for warming up the diesel engine, it is possible to switch on electrical loads until the temperature of the diesel engine exceeds a second limit value T2. The connection of electrical consumers increases the load of the diesel engine and thereby contributes to more rapid warming up. Preferably, in this case, those electrical consumers are connected the activity of which cannot be detected by the driver, that is to say, for example, the windshield heating or the glow plugs. When the third temperature limit value is reached, these consumers are switched off or are reset to the value predetermined by the driver.
The invention relates, furthermore, to a regulating arrangement for the cab heating and the diesel engine of a motor vehicle, the regulating arrangement being coupled to a temperature sensor for the temperature T of the diesel engine, to a pressure sensor for the intake pressure MAP of the diesel engine and to a controllable throttle valve for the supply of air to the diesel engine. The regulating arrangement is set up in such a way that it can carry out a method of the type explained above. That is to say, the regulating arrangement measures the temperature T of the diesel engine directly or indirectly via the temperature sensor, and, if this temperature is below a first limit value T1, the supply of air to the diesel engine is reduced via the throttle valve, in such a way that a currently predetermined value MAP_ref for the intake pressure is reached. Adherence to this value for the intake pressure may be checked and regulated via the pressure sensor. By means of a regulating arrangement of this type, a rapid heating of a cooled cab of a motor vehicle is possible, since the diesel engine runs through a speeded-up warm-up stage.